Electromagnetic shielding defect monitoring system and method for using the same

ABSTRACT

An embodiment disclosed herein is directed to a method of monitoring an electromagnetic shield effectiveness comprising transmitting a first electromagnetic field toward a first surface of an electromagnetic shield, detecting a second electromagnetic field transmitted from a second surface of the electromagnetic shield, generating a first signal corresponding to the second electromagnetic field and determining whether a defect exists at the electromagnetic shield by comparing the first signal to a predetermined threshold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.patent application Ser. No. 11/468,755, filed Aug. 30, 2006 andpublished on Mar. 27, 2008 as US Patent Application Publication No.2008/0074123, the entirety of which are incorporated herein byreference.

BACKGROUND

1. Field of Invention

Embodiments exemplarily disclosed herein relate to systems and methodsfor locating faults in electromagnetic shielding.

2. Discussion of the Related Art

In order to protect the circuit components of electronic equipment frompotentially damaging electromagnetic radiation, such as anexternally-sourced electromagnetic pulse (EMP) or other interferencesignals such as radar, broadcast radio and television, cellular phone,etc., it is customary to house electronic equipment within some form ofelectromagnetically shielded enclosure (e.g., a cabinet, a room, abuilding, etc., collectively referred to herein as an “enclosure”). Oncethe electronic equipment has been housed, the shielding effectiveness ofthe enclosure should be verified.

Conventionally, the shielding effectiveness of an enclosure is testedbefore installing electronic equipment therein. The shieldingeffectiveness of the enclosure can be tested in a laboratory setting orin the “real world” where the enclosure is deployed for use. Subsequentto testing, it is typically assumed that the shielding effectiveness ofthe enclosure will remain the same over time. It is, however, notuncommon that the shielding effectiveness of any enclosure will degradeover time. Indeed, there is a government agency “verification”requirement (MIL-STD-188-125) that mandates the ability to test theshielding effectiveness of enclosures after the enclosure has beendeployed and after electronic equipment has been housed therein. Suchtesting can be made very difficult or impossible simply due to thelocation in which the enclosure is deployed. For example, enclosures areoften deployed to remote locations such as Antarctica, deserted islands,jungles, mountain peaks, and other similar locations that are difficultto access and/or are inhospitable to humans as well as to the enclosuresthemselves. Thus, this strict verification requirement can create manyproblems that are typically encountered when attempting to conducton-site testing of the shielding-effectiveness of the enclosure.

The primary purpose of electromagnetic shielding is to substantiallyreduce exterior incident magnetic and electric fields by several ordersof magnitude to protect internal equipment from interference or damage.Likewise, electromagnetic shielding is also used to contain internallygenerated electric and magnetic fields to prevent exterior equipmentfrom being affected by the fields.

SUMMARY

Several embodiments exemplarily disclosed herein advantageously addressthe needs above as well as other needs by providing a system formonitoring effectiveness of an electromagnetic shield and a method forusing the same.

One embodiment exemplarily described herein is directed to a method ofmonitoring an electromagnetic shield effectiveness that includestransmitting a first electromagnetic field toward a first surface of theelectromagnetic shield, detecting a second electromagnetic fieldtransmitted from a second surface of the electromagnetic shield,generating a first signal corresponding to the second electromagneticfield, and determining whether a defect exists at the electromagneticshield by comparing the first signal to a predetermined threshold.

Another embodiment exemplarily described herein is directed to a systemfor monitoring effectiveness of an electromagnetic shield that includesa transmit system, a receiver system, and analysis circuitry. Thetransmit system is adapted to transmit a first electromagnetic fieldtoward a first surface of the electromagnetic shield. The receiversystem is adapted to detect a second electromagnetic field transmittedfrom a second surface of the electromagnetic shield, and the analysiscircuitry is adapted to determine whether a defect exists at theelectromagnetic shield by comparing a first signal corresponding to thesecond electromagnetic field to a predetermined threshold. In oneembodiment the system further comprises, control circuitry adapted tocontrol the operations of the transmit system and the receiver system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the embodiments exemplarilydisclosed herein will be more apparent from the following moreparticular description thereof, presented in conjunction with thefollowing drawings.

FIG. 1 illustrates one exemplary embodiment of an electromagneticshielding defect monitoring system;

FIG. 2 diagrammatically illustrates quasi-static and radiative regionsof an electromagnetic field transmitted from the second surface of anenclosure having a defect;

FIG. 3 illustrates one exemplary embodiment of the transmit system shownin FIG. 1;

FIG. 4 illustrates one exemplary embodiment of the receive system shownin FIG. 1;

FIG. 5 illustrates an exemplary functional block diagram of thecontroller system shown in FIG. 1, according to one embodiment; and

FIG. 6 exemplarily describes one embodiment of a method for monitoringelectromagnetic shielding defects.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings. Skilled artisans willappreciate that elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale. For example,the dimensions of some of the elements in the figures may be exaggeratedrelative to other elements to help to improve understanding of variousembodiments exemplarily disclosed herein. Also, common butwell-understood elements that are useful or necessary in a commerciallyfeasible embodiment are often not depicted in order to facilitate a lessobstructed view of these various embodiments exemplarily disclosedherein.

DETAILED DESCRIPTION

The following description is not to be taken in a limiting sense, but ismade merely for the purpose of describing the general principles ofexemplary embodiments. The scope of the invention should be determinedwith reference to the claims.

FIG. 1 illustrates one exemplary embodiment of an electromagneticshielding defect monitoring system.

As shown in FIG. 1, an exemplary electromagnetic shielding defectmonitoring system 100 includes a transmit system 102, a receive system104, a controller system 106, an RF spectrum analyzer 108, transmit andreceive control linkages 110 and 112, respectively, (collectivelyreferred to herein as “control linkages”), detect and analysis outputlinkages 114 and 116, respectively, (collectively referred to herein as“output linkages”), and a network connection 118. Also shown in FIG. 1is a partial view of an enclosure 120, having a first surface 122 and asecond surface 124, and a user interface 126.

As generally illustrated in FIG. 1, the transmit system 102 is coupledto the controller system 106 via the transmit control linkage 110, thereceive system 104 is coupled to the controller system 106 and the RFspectrum analyzer 108 via the receive control linkage 112 and the detectoutput linkage 114, respectively. The RF spectrum analyzer 108 isfurther coupled to the controller system 106 via the analysis outputlinkage 116. The controller system 106 is coupled to the user interface126 via the network connection 118.

The enclosure 120 defines a cavity having a low quality or “Q” factor,within which electronic equipment (not shown) such as computers,sensors, etc., may be housed. In one embodiment, the first surface 122is an exterior surface of the enclosure 120 and the second surface 124is an interior surface of the enclosure 120. As used herein, the term“exterior surface” generally refers to a set of enclosure surfaces thatare exposed to environmental conditions outside the enclosure 120.Similarly, as used herein, the term “interior surface” generally refersto a set of enclosure surfaces that are exposed to environmentalconditions inside the enclosure 120. In another embodiment, the firstsurface 122 is the interior surface of the enclosure 120 and the secondsurface 124 is the exterior surface of the enclosure 120.

The transmit system 102 is adapted to transmit a first electromagneticfield toward the first surface 122, thereby generating a first currenton the first surface 122 of the enclosure 120. A defect in the enclosure120 (e.g., an aperture in the enclosure 120, a thin area in theenclosure, etc.) electrically couples the first surface 122 with thesecond surface 124, thereby inducing a second current on the secondsurface 124. As a result, a second electromagnetic field is transmittedfrom the second surface 124 based upon the second current. The frequencyand amplitude of the second electromagnetic field corresponds to theseverity of the defect in the enclosure 120. The second electromagneticfield can be characterized by a radiative region and a quasi-staticregion.

FIG. 2 diagrammatically illustrates quasi-static and radiative regionsof the second electromagnetic field transmitted from the second surfaceof an enclosure having a defect, according to one embodiment.

Shown in FIG. 2 are a defect 202 in the enclosure 120 (e.g., in anexemplary form of an aperture extending through the first and secondsurfaces 122 and 124 of the enclosure 120), a first current 204generated on the first surface 122 of the enclosure 120 by a firstelectromagnetic field (not shown) transmitted toward the first surface122 by the transmit system 102 (not shown), and a second electromagneticfield 206 transmitted from the second surface 124 of the enclosure 120by a second current (not shown) induced on the second surface 124 thatis coupled to the first current 204 via defect 202. As illustrated, thesecond electromagnetic field 206 can be characterized as having aquasi-static region 208 (i.e., represented by the dashed line) and aradiative region 210 (i.e., represented by the square dot isopotentiallines). Generally, the field strength of the second electromagneticfield 206 in the quasi-static region 208 decreases rapidly withincreasing distance from the defect 202 while the field strength of thesecond electromagnetic field 206 in the radiative region 210 decreasesslowly with increasing distance from the defect 202.

Referring back to FIG. 1, the receive system 104 is adapted to detectthe frequency and amplitude of the second electromagnetic field 206transmitted from the second surface 124 of the enclosure 120. In oneembodiment, the receive system 104 is adapted to detect the frequencyand amplitude of the second electromagnetic field in both the radiativeand quasi-static regions 208 and 210, respectively. Upon detecting thefrequency and amplitude of the second electromagnetic field 206, thereceive system 104 generates a detected signal that contains detecteddata (i.e., data representing the detected frequency and amplitude ofthe radiative and quasi-static regions 208 and 210, respectively, of thesecond electromagnetic field 206).

The controller system 106 contains control circuitry adapted to controloperations of the transmit and receive systems 102 and 104,respectively, during a test procedure in which the presence and/orlocation of defects within the enclosure 120 is determined. The controlcircuitry may control operations of the transmit and receive systems 102and 104, respectively, either automatically or in response to commandsreceived from the user interface 126 via the network connection 118. Asused herein, the term “circuitry” refers to any type ofcomputer-executable instructions that can be implemented, for example,as hardware, firmware, and/or software, which are all within the scopeof the various teachings described.

As will also be discussed in greater detail below, the controller system106 further contains analysis circuitry adapted to determine whether adefect in the enclosure 120 exists and identify the location of thedefect in the enclosure 120 based upon operations of the transmit andreceive systems 102 and 104, respectively, and also based upon theanalysis signal generated by the RF spectrum analyzer 108.

The RF spectrum analyzer 108 is adapted to receive the detected signal,analyze the detected data contained therein, and generate an analysissignal based upon analysis of the detected data. Accordingly, theanalysis signal may contain quantified detected data representing thefrequency and amplitude of the second electromagnetic field in both theradiative and quasi-static regions of the second electromagnetic field.The RF spectrum analyzer 108 may be disposed within the enclosure 120 oroutside the enclosure 120. In one embodiment, the RF spectrum analyzermay be provided as any commercially available spectrum analyzer with aresolution bandwidth (RBW) of 10 Hz, capable of being controlled over aLAN, and be sensitive to signals over a range of frequencies betweenabout 10 kHz to about 100 GHz.

The transmit control linkage 110, receive control linkage 112, detectoutput linkage 114, and analysis output linkage 116 may be provided asone or more fiber optic communication lines, one or more copper lines,or the like, or combinations thereof. In one embodiment, the transmitand receive control linkage 110 and 112, respectively, may comprise aGeneral Purpose Instrumentation Bus (GPIB).

The network connection 118 may be any suitable connection to a network(e.g., a PAN, a LAN, or a WAN), enabling a user to control operations ofthe electromagnetic shielding defect monitoring system 100 via thecontroller via the user interface 126.

The user interface 126 may be any device (e.g., a personal computer, alaptop computer, a personal digital assistant, etc.) adapted tocommunicate with the controller system 106 via the network connection118.

Although FIG. 1 illustrates the controller system 106 coupled to onlyone set of transmit and receive systems 102 and 104, respectively, viatransmit and receive control linkages 110 and 112, respectively, it willbe appreciated that, in other embodiments, the controller system 106 maybe coupled to any number of sets of other transmit and receive systemsvia corresponding transmit and receive control linkages associated withthe other sets of transmit and receive systems. Accordingly, thecontroller system 106 exemplarily disclosed herein may be adapted tocontrol operations of transmit and receive systems associated withmultiple enclosures.

FIG. 3 illustrates one exemplary embodiment of the transmit system shownin FIG. 1.

As shown in FIG. 3, an exemplary transmit system 102 includes an RFspectrum source 302, an RF amplifier 304, a transmit switching matrix306, and a plurality of transmit antennas 308 a to 308 n (genericallyreferred to as transmit antennas 308).

As illustrated, the RF spectrum source 302, the RF amplifier 304, andthe transmit switching matrix 306 are each coupled to the transmitcontrol linkage 110. The RF spectrum source 302 is further coupled tothe RF amplifier 304, the RF amplifier 304 is further coupled to thetransmit switching matrix 306, and the transmit switching matrix 306 isfurther coupled to the plurality of transmit antennas 308 a to 308 n.

Although FIG. 3 illustrates the transmit system 102 as comprising, amongother elements, the transmit switching matrix 306, it will beappreciated that the transmit system 102 shown in FIG. 3 mayalternatively be provided without such a component. In such anembodiment, each transmit antenna 308 may be coupled directly to thetransmit control linkage 110 and the RF amplifier 304 (e.g., as shown at310).

As described in various embodiments above, the first surface 122 may beeither an exterior or an interior surface of the enclosure 120.Accordingly, where the first surface 122 is an exterior surface, thetransmit antennas 308 are disposed outside the enclosure 120. However,where the first surface 122 is an interior surface, the transmitantennas 308 are disposed inside the enclosure 120. In either case, thetransmit antennas 308 are permanently installed with respect to theenclosure 120 such that they are positionally fixed relative to theenclosure 120.

The RF spectrum source 302 is adapted to control the frequency of an RFsignal (i.e., the first electromagnetic field) transmitted by anactivated transmit antenna 308 onto the first surface 122. In oneembodiment, the RF spectrum source 302 may be provided as anycommercially available spectrum source having an output power ratio ofabout +15 dBm and adapted to control the frequency of the RF signal(i.e., the first electromagnetic field) transmitted by each transmitantenna 308 to be between about 10 kHz and about 100 GHz.

The RF amplifier 304 is adapted to control the amplitude of the RFsignal (i.e., the first electromagnetic field) transmitted by anactivated transmit antenna 308 toward the first surface 122 of theenclosure 120. In one embodiment the RF amplifier 304 is comprised ofany suitable combination of a commercially available pre-amplifier (notshown) and a commercially available amplifier (not shown) coupled to thepre-amplifier. In such an embodiment, the pre-amplifier may be operablewithin a frequency range of about 0.01-100 GHz, have a gain of about 25dB, and have an output power ratio of about +20 dBm and the amplifiermay be operable within a frequency range of about 0.01-100 GHz, have again of about 30 dB, and have an output power ratio of about +35 dBm.

The transmit switching matrix 306 is adapted to activate at least one ofthe transmit antennas 308. In one embodiment, the transmit switchingmatrix 306 comprises a transmit switch control module (not shown), aswitch driver (not shown) coupled to the transmit switch control module,and an RF switch array (not shown) coupled to the switch driver. Thetransmit switch control module receives transmit control signals fromthe controller system 106 via the transmit control linkage 110 andgenerates corresponding switch control signals. The switch driverresponds to the switch control signals generated by the transmit switchcontrol module by driving the switch array to selectively activate atleast one of the transmit antennas 308. In embodiments where thetransmit switching matrix 306 is not comprised within the transmitsystem 102, each transmit antenna 308 within the transmit system 102remains activated during the entire test procedure.

Any desired number of transmit antennas 308 (e.g., n=1, 2, 3, 4, 5,etc.) may be comprised within the transmit system 102. In oneembodiment, the number of transmit antennas 308 comprised within thetransmit system 102 may correspond to the number of antennas capable ofdirectly illuminating the total surface area of the first surface 122.Each of the transmit antennas 308 is arranged operably proximate to thefirst surface 122 of the enclosure 120 (e.g., within about 2 to 3 metersfrom the first surface 122) and, when activated, is adapted to transmitan RF signal (i.e., a first electromagnetic field) toward the firstsurface 122 of the enclosure 120.

In one embodiment, each of the transmit antennas 308 may be provided asany commercially available isotropic antenna adapted to transmit RFsignals (i.e., electromagnetic fields) over a signal-to-noise range ofat least about 100 dB. For example, each transmit antenna 308 may beprovided as a 5 dBi antenna with a type N connector.

FIG. 4 illustrates one exemplary embodiment of the receive system shownin FIG. 1.

As shown in FIG. 4, an exemplary receive system 104 includes a low noiseamplifier 402, an RF attenuator 404, a receive switching matrix 406 anda plurality of receive antennas 408 a to 408 m (generically referred toas receive antennas 408).

As illustrated, the RF attenuator 404 and the receive switching matrix406 are each coupled to the receive control linkage 112. The low noiseamplifier 402 is coupled to the detect output linkage 114 and to the RFattenuator 404, the RF attenuator 404 is further coupled to the receiveswitching matrix 406, and the receive switching matrix 406 is furthercoupled to the plurality of receive antennas 408.

Although FIG. 4 illustrates the receive system 104 as comprising, amongother elements, a receive switching matrix 406, it will be appreciatedthat the receive system 104 shown in FIG. 4 may alternately be providedwithout such a component. In such an embodiment, each receive antenna408 may be coupled directly to the receive control linkage 112 and theRF attenuator 404 (e.g., as shown at 410). In view of the above, it willbe appreciated that both the transmit and receive systems 102 and 104,respectively, may comprise transmit and receive switching matrices 306and 406, respectively; only one of the transmit and receive systems 102and 104, respectively, may comprise a switching matrix; or none of thetransmit and receive systems 102 and 104, respectively, may comprisetransmit and receive switching matrices 306 and 406, respectively.

As described in various embodiments above, the second surface 124 may beeither an interior or an exterior surface of the enclosure 120.Accordingly, where the second surface 124 is an interior surface of theenclosure 120, the receive antennas 408 are disposed inside theenclosure 120. However, where the second surface 124 is an exteriorsurface of the enclosure 120, the receive antennas 408 are disposedoutside the enclosure 120. In either case, the receive antennas 408 arepermanently installed with respect to the enclosure 120 such that theyare positionally fixed relative to the enclosure 120.

The low noise amplifier 402 is adapted to amplify detected signalsgenerated by activated ones of the plurality of receive antennas 408 andpassed by the RF attenuator 404. Detected signals amplified by the lownoise amplifier 402 are transmitted to the RF spectrum analyzer 108 viathe detect output linkage 114.

The RF attenuator 404 is adapted to reduce the amplitude or power ofdetected signals generated by activated ones of the plurality of receiveantennas 408 without appreciably distorting their waveforms. In oneembodiment, the RF attenuator 404 is a programmable attenuatorcomprising an attenuator control module (not shown), an attenuatordriver (not shown) coupled to the attenuator control module, and anadjustable attenuator (not shown) coupled to the attenuator driver. Theattenuator control module receives receive control signals from thecontroller system 106 via the receive control linkage 112 and generatescorresponding attenuator control signals. The attenuator driver respondsto the attenuator control signals generated by the attenuator controlmodule by driving the adjustable attenuator to selectively adjust thedegree to which the detected signal is attenuated. In one embodiment,the RF attenuator 404 may be provided as substantially any suitableattenuator having an attenuation range between about 0 dB to about 70 dBand a frequency range from DC to about 100 GHz.

The receive switching matrix 406 is adapted to activate at least one ofthe receive antennas 408. In one embodiment, the receive switchingmatrix 406 comprises a receive switch control module (not shown), aswitch driver (not shown) coupled to the switch control module, and anRF switch array (not shown) coupled to the switch driver. The receiveswitch control module receives receive control signals from thecontroller system 106 via the receive control linkage 112 and generatescorresponding switch control signals. The switch driver responds to theswitch control signals generated by the receive switch control module bydriving the switch array to selectively activate at least one of thereceive antennas 408. In embodiments where the receive switching matrix406 is not comprised within the receive system 104, each receive antenna408 within the receive system 104 remains activated during the entiretest procedure.

Any desired number of receive antennas 408 (e.g., m=1, 2, 3, 4, 5, etc.)may be comprised within the receive system 104. In one embodiment, thenumber of receive antennas 408 in the receive system 104 exceeds thenumber of transmit antennas 308 in the transmit system 102 (i.e., m>n).In another embodiment, the number of transmit antennas 308 in thetransmit system 102 exceeds the number of receive antennas 408 in thereceive system 104 (i.e., n>m). In one embodiment, the number of receiveantennas 408 comprised within the receive system 104 may be enough tocover correspond to the total surface area of the second surface 124.Each of the receive antennas 408 is arranged operably proximate to thesecond surface 124 of the enclosure 120 (e.g., within about 1 to 2meters from the second surface 124) and, when activated, is adapted toreceive an RF signal (i.e., a second electromagnetic field) transmittedfrom the second surface 124 and to detect the second electromagneticfield induced on the second surface 124 of the enclosure 120. Each ofthe receive antennas 408 is arranged operably proximate to the secondsurface 124 of the enclosure 120 and, when activated, are adapted todetect the frequency and amplitude of the second electromagnetic field206 in both the aforementioned radiative and quasi-static regions 208and 210, respectively, and generate a detected signal corresponding tothe frequency and amplitude detected.

In one embodiment, each of the receive antennas 406 may be provided asany commercially available isotropic antenna adapted to receive RFsignals (i.e., electromagnetic fields).

FIG. 5 illustrates an exemplary functional block diagram of thecontroller system 106 shown in FIG. 1, according to one embodiment.

As shown in FIG. 5, the controller system 106 includes theaforementioned control circuitry 502, the aforementioned analysiscircuitry 504, in addition to memory 506. Also shown in FIG. 5 are theaforementioned transmit and receive control linkages 110 and 112,respectively, the analysis output linkage 116, and the networkconnection 118.

The control circuitry 502 is coupled to the transmit and receive controllinkages 110 and 112, respectively, the network connection 118, and thememory 506. The analysis circuitry 504 is further coupled to theanalysis output linkage 116, the network connection 118, and the memory506. As used herein, the term “memory” is intended to refer to anycomputer-readable storage medium and/or device such as read accessmemory (RAM), read only memory (ROM), a hard disk drive, opticaldisk/optical disk drive, magnetic disk/magnetic disk drive, and thelike, and combinations thereof.

As discussed above, the control circuitry 502 is adapted to controloperations of the transmit system 102 and the receive system 104 duringa test procedure. Accordingly, and in one embodiment, the controlcircuitry 502 is adapted to control operations of the transmit system102 exemplarily described with respect to FIG. 3 by driving the RFspectrum source 302 to cause an activated transmit antenna 308 to directan RF signal (i.e., a first electromagnetic field) of a particularfrequency toward the first surface 122, driving the RF amplifier 304 tocause an activated transmit antenna 308 to direct an RF signal (i.e., afirst electromagnetic field) having a particular amplitude, and drivingthe transmit switching matrix 306 to activate one or more particulartransmit antennas 308. In embodiments where the transmit system 102 doesnot comprise the transmit switching matrix 306, transmit antennas 308are simply activated when the RF spectrum source 302 and RF amplifier304 are driven.

In one embodiment, the control circuitry 502 may drive the RF spectrumsource 302, the RF amplifier 304, and the transmit switching matrix 306(when comprised within the transmit system 102) as described above bygenerating various transmit control signals and communicating thetransmit control signals to the RF spectrum source 302, the RF amplifier304, and the transmit switching matrix 306, via the transmit controllinkage 110.

For example, the control circuitry 502 may be adapted to drive the RFspectrum source 302 to control the frequency of the RF signal (i.e., thefirst electromagnetic field) transmitted by an activated transmitantenna 308 to be at least a minimum frequency, F₀. In one embodiment,the minimum frequency, F₀ may correspond to physical dimensions of theenclosure 120, to shielding requirements of the enclosure 120, or thelike, or combinations thereof. For example, the minimum frequency F₀ maybe determined according to the formula:

F_(o) = 300/4 L,

where L is the maximum dimension of the enclosure 120 in x, y, or zCartesian coordinates. In such an embodiment, the value for L may beinput by the user (e.g., via the user interface 126).

In another embodiment, the control circuitry 502 is adapted to drive theRF spectrum source 302 to vary the frequency of the RF signal (i.e., thefirst electromagnetic field) transmitted by an activated transmitantenna 308. In such an embodiment, the control circuitry 502 may drivethe RF spectrum source 302 to vary the frequency of the RF signal (i.e.,the first electromagnetic field) transmitted by an activated transmitantenna 308 at a plurality of frequency points having frequenciesranging from F₀ (or 10 kHz, whichever is greater) to about 100 GHz, witha dwell time for each frequency point of about 9 seconds or less.Further, the total number of frequency points used is variable anddepends upon the step size between successive frequency points. Forexample, the step size between successive frequency points may be about5% or less of the absolute frequency. In one embodiment, the controllersystem 106 may be adapted to drive the RF spectrum source 302 to varythe frequency of the RF signal (i.e., the first electromagnetic field)transmitted by an activated transmit antenna 308 with frequency pointsat a predetermined step size. In another embodiment, the step sizebetween successive frequency points may be input/modified by the user(e.g., via the user interface 126). The amount of time required totransmit an RF signal (i.e., a first electromagnetic field), having theplurality of frequencies as described above, at the first surface 122may be referred to herein as a “test period.”

In one embodiment, the control circuitry 502 is adapted to drive thetransmit switching matrix 306 to sequentially activate one or moretransmit antennas 308. In such an embodiment, the control circuitry 502may drive the transmit switching matrix 306 to activate one or moretransmit antennas 308 for a duration sufficient to allow the activatedtransmit antenna(s) to transmit RF signals (i.e., first electromagneticfields) at the plurality of frequency points having frequencies rangingfrom F₀ (or 10 kHz, whichever is greater) to about 100 GHz.

In one embodiment, the control circuitry 502 generates theaforementioned transmit control signals upon being instructed to do soby commands generated at the user interface and communicated to thecontroller system 106 via the network connection 118. In anotherembodiment, the control circuitry 502 generates the aforementionedtransmit control signals automatically according to, for example, apredetermined schedule stored in memory 506.

As discussed above, the control circuitry 502 is adapted to controloperations of the receive system 104 during a test procedure.Accordingly, and in one embodiment, control circuitry 502 is adapted tocontrol operations of the receive system 104 exemplarily described withrespect to FIG. 3 by driving the receive switching matrix 406 toactivate one or more particular receive antennas 408, driving the RFattenuator 404 to adjust the attenuation settings thereof, and drivingthe receive switching matrix 406 to activate one or more particularreceive antennas 408. In embodiments where the receive system 104 doesnot comprise the receive switching matrix 406, receive antennas 408 aresimply activated when the RF spectrum source 302 and RF amplifier 304are driven.

In one embodiment, the control circuitry 502 may drive the RF attenuator404 and the receive switching matrix 406 (when included within thereceive system 104) by generating a receive control signal andcommunicating the receive control signal to the receive switching matrix406 and RF attenuator 404, via the receive control linkage 112.

For example, the control circuitry 502 is adapted to drive the receiveswitching matrix 406 to sequentially activate a receive antenna 308 whenone or more transmit antennas 308 are activated. In such an embodiment,the control circuitry 502 may drive the receive switching matrix 406 toactivate one receive antenna 408 for a duration equal to one test periodassociated with one or more activated transmit antennas 306. In anotherembodiment, the control circuitry 502 may drive the receive switchingmatrix 406 to activate one receive antenna 408 for a duration equal totest periods associated with sequentially activated transmit antennas306 comprised within the transmit system 102.

In one embodiment, the control circuitry 502 generates theaforementioned receive control signals upon being instructed to do so bycommands generated at the user interface and communicated to thecontroller system 106 via the network connection 118. In anotherembodiment, the control circuitry 502 generates the aforementionedreceive control signals automatically according to, for example, apredetermined schedule stored in memory 506.

As described above, the analysis circuitry 504 is adapted determinewhether a defect in the enclosure 120 exists and identify the locationof the defect in the enclosure 120.

In one embodiment, the analysis circuitry 504 is adapted to determinethe general location of the defect within the enclosure 120 based, atleast in part, upon the field strength of the radiative region 210 ofthe second electromagnetic field 206 as detected by an activated receiveantenna 408. Assuming that an activated receive antenna 408 detects anelectromagnetic field having a strength that is proportional to antennavoltage, the shielding effectiveness, SE, of the enclosure 120 can bedetermined according to Equation 1:

$\begin{matrix}{{{SE} = {20\mspace{14mu} {\log ( \frac{V_{c}}{V_{t}} )}}},} & {{Eq}.\mspace{14mu} (1)}\end{matrix}$

where V_(t) represents the signal strength of an analysis signalgenerated during a test procedure in which an RF signal (i.e., a firstelectromagnetic field) having a predetermined frequency and polarizationis transmitted by a transmit antenna 308 toward the enclosure 120 andwhere V_(c) represents the signal strength of an analysis signalgenerated during a calibration procedure in which an RF signal (i.e., afirst electromagnetic field) having the predetermined frequency andpolarization was transmitted by a transmit antenna 308 directly to thereceive antenna 408. Corrections may be applied for any differences ininstrumentation system, gain, or attenuation between the calibration andtest procedures.

Accordingly, during a test procedure, the analysis circuitry 504receives data indicating the signal strength V_(t) of the analysissignal from the RF spectrum analyzer 108 via the analysis output linkage116, calculates an SE value using the signal strength V_(t) and thepredetermined calibration value V_(c). The calculated SE of theenclosure during the test procedure is then compared with a presetthreshold SE value. If results of the comparing indicate that the presetthreshold shield effectiveness value is less than the determined shieldeffectiveness, SE, it is inferred that a defect exists within theenclosure 120. Subsequently, the analysis circuitry 504 determines thelocation of the defect in the enclosure 120.

In one embodiment, the analysis circuitry 504 is adapted to determinethe precise location of the defect within the enclosure 120 based, atleast in part, upon the field strength of the radiative region 210 ofthe second electromagnetic field 206 as detected by an activated receiveantenna 408. The precision to which the location of a defect isdetermined (i.e., the quasi-static detection limit) can be increased byincreasing the frequency of the RF signal (i.e., the firstelectromagnetic field) transmitted by an activated transmit antenna 308,and thus the frequency of the second electromagnetic field 206, as shownby the experimentally obtained values presented in Table 1 below:

TABLE 1 Wavelength Frequency of of RF Signal RF Signal Quasi-StaticQuasi-Static (Hz) (m) Detection Limit (m) Detection Limit (in) 4.25 ×10⁸ 7.06 × 10⁻¹ 0.11 4.42 5.25 × 10⁸ 5.71 × 10⁻¹ 0.09 3.58 7.25 × 10⁸4.14 × 10⁻¹ 0.07 2.59 9.25 × 10⁸ 3.24 × 10⁻¹ 0.05 2.03

In one embodiment, the analysis circuitry 504 identifies the preciselocation of the defect using operational variables of the transmit andreceive systems 102 and 104, respectively, and analysis signalsgenerated during the test procedure, as inputs of a triangulationprocedure.

For example, the control circuitry 502 outputs transmit and receivecontrol signals adapted to drive the transmit and receive systems 102and 104, respectively, to activate one or more transmit antennas 308 insynchrony with one or more receive antennas 408 until a desired numberof combinations or types of combinations of activated transmit/receiveantennas 308/408 has been obtained. Data identifying each activatedtransmit and receive antenna 308 and 408, respectively, (i.e., transmitantenna selection data and receive antenna selection data, respectively)is stored within memory 506. Additionally, the control circuitry 502outputs transmit control signals adapted to drive the RF spectrum source302 and the RF amplifier 304 to cause the RF signals (i.e., the firstelectromagnetic fields) transmitted directed by the transmit antennas tohave a particular frequency and amplitude. Data representing thefrequency and amplitude of each RF signal (i.e., first electromagneticfield) transmitted by each activated transmit antenna 308 (i.e.,transmit frequency data and transmit amplitude data, respectively) isalso stored within memory 506 and is correlated with transmit antennaselection and receive antenna selection data. An analysis signal isgenerated by the RF spectrum analyzer 108 for each combination ofactivated transmit/receive antennas 308/408 and is communicated to theanalysis circuitry 504. Quantified detected data within the analysissignal representing the frequency and amplitude of the quasi-staticregion or the radiative region of the second electromagnetic field isthen stored within the memory 506 and correlated with the transmitantenna selection data, receive antenna selection data, transmitfrequency data, and transmit amplitude data. After operations of thetransmit and receive systems 102 and 104 have been controlled asdesired, the analysis circuitry 504 accesses the memory 506 andidentifies the location of the defect in the enclosure 120 according toany suitable triangulation method.

FIG. 6 exemplarily describes one embodiment of a method for monitoringelectromagnetic shielding defects according to the aforementioned testprocedure.

The illustrated test procedure begins at 602. At 604, a firstelectromagnetic field is transmitted toward the first surface 122 of theenclosure 120. As described above, the first electromagnetic field maybe generated upon the controller system 106 outputting transmit controlsignals to control operations of the various components of the transmitsystem 102 via the transmit control linkage 110.

At 606, a second electromagnetic field transmitted from the secondsurface 124 of the enclosure 120 is detected. As described above, thesecond electromagnetic field may be detected upon the controller system106 outputting receive control signals to control operations of thevarious components of the receive system 104 via the receive controllinkage 112. Detected signals, corresponding to the detected secondelectromagnetic field, are output by the receive system 104 to the RFspectrum analyzer 108 via the detect output linkage 114. Analysissignals, corresponding to the detected signals, are output by the RFspectrum analyzer 108 to the controller system 106 via the analysisoutput linkage 116.

At 608, it is determined whether a defect exists within the enclosure120. As described above, the analysis circuitry 504 is adapted todetermine whether a defect exists within the enclosure 120 by comparingthe analysis signal output by the RF spectrum analyzer 108 with apredetermined calibration value.

If it is determined that a defect does exist then, at 610, the locationof the defected within the enclosure 120 is determined. In oneembodiment, a defect detection alarm signal may be communicated from thecontroller system 106 to the user interface 126 via the networkconnection 118 upon determining that a defect exists within theenclosure 120. The defect detection alarm signal may cause the userinterface 126 to alert a user of the user interface 126 to the fact thata defect has been detected within the enclosure 120. As described above,the location of a defect is determined by employing a triangulationprocedure using operational variables of the transmit and receivesystems 102 and 104, respectively, and analysis signals output by the RFspectrum analyzer 108, as inputs of a triangulation procedure. In oneembodiment, a defect location signal may be communicated from thecontroller system 106 to the user interface 126 via the networkconnection 118 upon determining the location of the defect within theenclosure 120. The defect location signal may cause the user interface126 to identify the location of the defect within the enclosure 120 to auser of the user interface 126. Subsequently, or if it is determinedthat a defect does not exist then, at 612, the test procedure ends.

In one embodiment, data generated during a test procedure may bearchived within memory 506 for record-keeping purposes. In anotherembodiment, data generated during a test procedure may be communicatedto the user interface 126 via the network connection 118 during or aftercompletion of the test procedure. Data generated during a test proceduremay be communicated to the user interface 126, for example, in the formof a plot of SE values derived from activated receive antennas 408versus frequency of RF signal directed by activated transmit antennas308.

Numerous embodiments have been exemplarily described above that providean electromagnetic shielding defect monitoring system adapted to detectshielding faults correlatable to, for example, MIL-STD-188-125 shieldingperformance requirements, trigger detection alarm signals if necessary,and provide a capability to precisely locate the shielding fault so thatcorrective maintenance can be applied.

While the numerous embodiments have been exemplarily described by meansof specific examples and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

1. A method of monitoring an electromagnetic shield effectivenesscomprising: transmitting a first electromagnetic field toward a firstsurface of the electromagnetic shield; detecting a secondelectromagnetic field transmitted from a second surface of theelectromagnetic shield; and generating a first signal corresponding tothe second electromagnetic field; and determining whether a defectexists at the electromagnetic shield by comparing the first signal to apredetermined threshold.
 2. The method of claim 1, wherein thedetermining whether a defect exists comprises calculating aneffectiveness value based on data contained within the first signal andcomparing the effectiveness value to the predetermined threshold.
 3. Themethod of claim 2, wherein the defect exists if the effectiveness valueexceeds the predetermined threshold.
 4. The method of claim 1, furthercomprising determining the location of the defect at the electromagneticshield when it is determined that the defect exists.
 5. The method ofclaim 1, wherein the first surface is an inner surface of theelectromagnetic shield, and the second surface is an outer surface ofthe electromagnetic shield.
 6. The method of claim 1, wherein the firstsurface is an outer surface of the electromagnetic shield, and thesecond surface is the inner surface of the electromagnetic shield. 7.The method of claim 1, wherein the transmitting the firstelectromagnetic signal comprises transmitting the first electromagneticsignal at a predetermined time corresponding to a predefined schedule.8. The method of claim 1, wherein the transmitting the firstelectromagnetic field further comprises generating a first current onthe first surface.
 9. The method of claim 7, wherein the secondelectromagnetic field is transmitted by a second current induced on thesecond surface by the first current.
 10. The method of claim 1, furthercomprising detecting a frequency and amplitude of the secondelectromagnetic field.
 11. The method of claim 10, further comprisinggenerating a second signal that contains data representing the detectedfrequency and amplitude of the second electromagnetic field; and Whereinthe generating the first signal comprises generating the first signalbased on the data of the second signal.
 12. The method of claim 1,wherein the second magnetic field comprises a quasi-static region and aradiative region; and Wherein the detecting the second electromagneticfield comprises detecting one or both the quasi-static region and theradiative region.
 13. A system for monitoring effectiveness of anelectromagnetic shield, comprising: a transmit system adapted totransmit a first electromagnetic field toward a first surface of theelectromagnetic shield; a receiver system adapted to detect a secondelectromagnetic field transmitted from a second surface of theelectromagnetic shield; and analysis circuitry adapted to determinewhether a defect exists at the electromagnetic shield by comparing afirst signal corresponding to the second electromagnetic field to apredetermined threshold.
 14. The system of claim 13, further comprisingcontrol circuitry adapted to control the operations of the transmitsystem and the receiver system.
 15. The system of claim 14, wherein thecontrolling the operations of the transmit system comprises controllingthe properties of the first electromagnetic field.
 16. The system ofclaim 14, wherein the control circuitry is further adapted to detect auser input entered through a user interface and to generate controlsignals to cause the transmit system to transmit the firstelectromagnetic field based on the user input.
 17. The system of claim14, wherein the control circuitry is further adapted to generate a usernotification adapted to be displayed through a user interface when thedefect exists.
 18. The system of claim 13, wherein the receiver systemis further adapted to determine a frequency and amplitude of the secondelectromagnetic field and further adapted to generate a signalcontaining the data corresponding to the determined frequency andamplitude.
 19. The system of claim 13, wherein the transmit systemcomprises plurality of transmit antennas; and the first electromagneticfield is transmitted through one of the plurality of antennas.
 20. Thesystem of claim 13, wherein the receiver system comprises plurality ofreceiver antennas; and the second electromagnetic field is detectedthrough one of the plurality of antennas.